Solar Rotation Nos: 2216 – 2217
A small welcome increase in sunspot activity. Active Region (AR)2738 was quite spectacular!
Here are the solar highlights for April 2019 together with a selection of images.
Sunspots
AR2737
This sunspot group of several small spots appeared over the east solar limb at the end of March. This group’s magnetic polarity and low latitude of +12°, showed it was of the old sunspot cycle (No. 24). By now in early April AR2737 was further onto the Sun’s disc but it had changed little despite a little development on the 2nd and went into decline as it headed westwards. AR2737 went over the west limb around the 8th.
AR2738
Appeared over the east limb on the 8th and despite its small size it seemed to be minor solar flare active and likely to develop further. It too was near the solar equator at latitude +6°. We did not have to wait long as AR2738 started to grow so that by the 10th it was sunspot type Cho just as it was nearing coming more onto the Sun’s disc. The main sunspot clearly showed a light bridge which split the sunspot’s dark central umbra into two unequal parts, something that was commented on by several observers. This light bridge was estimated to be about 20,000km long! AR2738 reached the Central Meridian (CM) on the 13th meaning the whole sunspot was now facing the Earth. No solar flares were seen but AR2738 did produce a lot of radio static at that time which could be detected here on Earth with the right equipment. There was not much change as it neared the west limb by the 18th.
AR2739
Was a small (type Bxo) twin-spot group that developed just a little way east of the larger AR2738 on the 18th. AR2739 was also a Cycle 24 group at the very low latitude of +5°. There was some development in region in the following days, but AR2739 then started to fade and went over the west limb on the 21st.
The Sun was spotless from the 22nd to the 30th April.
SPA Sunspot Mean Daily Frequency (MDF): 0.64 (was 0.44).
SPA Relative Sunspot Number: 6.55 (was 5.59).
Solar Prominences, Plage, Filaments and Flares
It was quite a month for solar hydrogen-alpha observing!
Prominences were well on view this month, especially on the 10th and 11th, but fell away towards the end of April. A filaprom was observed on the 5th just off the east limb. Several prominences were seen on the 6th and on the 8th another taller filaprom was visible on the west limb. The 10th saw a huge broad arch-type prominence on the north limb and smoke-stack and pillar types along south east limb. By the following day, there was a lot of prominence activity along the north west and east limbs and extensive bright plage and filament activity around AR2738 too! More smoke-stack and pillar type prominences appeared over the east limb on the 20th. More proms were seen on the east limb on the 22nd and again on the 23rd and 24th and on the 25th a row of detached prominences were visible along the east limb!
Bright plage and filament activity persisting in the region of AR2737 up to the 7th even though no spots were seen after the 5th. It was AR2738 that was really striking as it brought with it a lot of widespread filaments and bright plage activity particularly to the east of the main sunspot.
SPA Prominence Mean Daily Frequency (MDF): 1.73 (was 1.94).
Well done to Alan Heath and Jonathan Shanklin, who observed 28 days, to Brian Gordon-States, who observed 27 days, and to Michael Fullerton and Ian Lee who both observed 26 days.
Detailed count records of Active Regions and Relative Sunspot Numbers came from: Brian Gordon-States, Michael Fullerton, Alan Heath, Ian Lee, Jonathan Shanklin and Bob Steele.
Images and drawings were supplied by: Mark Beveridge, Carl Bowron, Paul Brierley, Ian Lee and Cliff Meredith.
Geoff Elston
Director